Magnesium OxyChloride (“MOC”) cement was developed by Stanislaus Sorel in 1867. This cement binder technology provides inherently excellent properties such as fire retardancy; mold, algae and insect resistance; high compressive strengths, tenacious bonding characteristics and unmatched impact resistance. Due to these and other excellent properties, MOC cements have found good, but limited utility when used as the binder system for a multitude of applications ranging from high strength construction boards, industrial monolithic flooring concretes, patch repair concretes and mortars, as the binder system for billiards balls and many other applications. The biggest limiting factor for increased use of MOC binder systems has been the inherent lack of water resistance during the early cure stages, e.g., during the first months of curing. This limiting performance property is accentuated when finished products are used for outdoor applications, or where exposure to water may occur even in interior applications.
Studies have shown that upon ingress of water into the MOC cement matrix, the water causes efflorescence, or leaching of the Magnesium Chloride (MgCl2) salt. The resultant matrix after leaching includes a higher concentration of Magnesium Hydroxide, which is a much weaker binder matrix than Magnesium OxyChloride.
Various technologies have been tried by many cement and concrete technologists with limited to no benefits. All of the known water resistant additives that are typically incorporated into Ordinary Portland Cement (“OPC”) mortars or concretes have either no effect, or will even worsen the MOC cement properties.
Another major problem associated with MOC cements is that chlorides are present in the cement matrix, even after full cure. These chloride ions can be highly detrimental (corrosive) to metals that are used to either fasten MOC-based construction panels, or to metals that may be used to reinforce concrete structures, such as steel reinforcing bars (rebar). This disclosure addresses the use of phosphates, and various nitrites such as Magnesium Nitrites, and/or various zeolite additives that overcome these corrosion issues. As an example, an exterior MOC construction wall board formulation with both water and corrosion resistance in accordance with the disclosure can include:
Composition:% by Weight:MgO - 3% active lightly calcined21MgCl2 - 220 Baume Solution15H2015MgH2PO4 (for water resistance)3Zeolite (for corrosion resistance)2Mg Nitrite (for corrosion resistance)3Expanded Polystyrene Beads (EPS)8Recycled carpet fibers11Fly Ash - Class C20Fiberglass Mesh Scrim2
Another issue associated with MOC cements is that although cure speed is much faster than conventional Portland cements, even faster cure speeds are desirable in applications such as construction board manufacturing and fast-setting repair mortars, etc. The use of the magnesium phosphate water resistant additive in combination with various metal oxide pigments, such as, for example, iron oxide, copper oxide, zinc oxide and titanium oxide, was found to have accelerated MOC cure times.